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fixed regexes to avoid ReDoS attacks #10

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merged 2 commits into from
May 25, 2021
Merged

fixed regexes to avoid ReDoS attacks #10

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09e1086
fixed regexes to avoid ReDoS attacks
jeffrey-pinyan-ithreat May 13, 2021
d8b5e6b
streamlined regexes, simplified parse() returns
jeffrey-pinyan-ithreat May 13, 2021
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1 change: 1 addition & 0 deletions .npmignore
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Original file line number Diff line number Diff line change
@@ -1,2 +1,3 @@
.travis.yml
redos.js
test.js
52 changes: 17 additions & 35 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,29 +2,14 @@

var isWindows = process.platform === 'win32';

// Regex to split a windows path into three parts: [*, device, slash,
// tail] windows-only
var splitDeviceRe =
/^([a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/]+[^\\\/]+)?([\\\/])?([\s\S]*?)$/;

// Regex to split the tail part of the above into [*, dir, basename, ext]
var splitTailRe =
/^([\s\S]*?)((?:\.{1,2}|[^\\\/]+?|)(\.[^.\/\\]*|))(?:[\\\/]*)$/;
// Regex to split a windows path into into [dir, root, basename, name, ext]
var splitWindowsRe =
/^(((?:[a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/]+[^\\\/]+)?[\\\/]?)(?:[^\\\/]*[\\\/])*)((\.{1,2}|[^\\\/]+?|)(\.[^.\/\\]*|))[\\\/]*$/;

var win32 = {};

// Function to split a filename into [root, dir, basename, ext]
function win32SplitPath(filename) {
// Separate device+slash from tail
var result = splitDeviceRe.exec(filename),
device = (result[1] || '') + (result[2] || ''),
tail = result[3] || '';
// Split the tail into dir, basename and extension
var result2 = splitTailRe.exec(tail),
dir = result2[1],
basename = result2[2],
ext = result2[3];
return [device, dir, basename, ext];
return splitWindowsRe.exec(filename).slice(1);
}

win32.parse = function(pathString) {
Expand All @@ -34,24 +19,24 @@ win32.parse = function(pathString) {
);
}
var allParts = win32SplitPath(pathString);
if (!allParts || allParts.length !== 4) {
if (!allParts || allParts.length !== 5) {
throw new TypeError("Invalid path '" + pathString + "'");
}
return {
root: allParts[0],
dir: allParts[0] + allParts[1].slice(0, -1),
root: allParts[1],
dir: allParts[0] === allParts[1] ? allParts[0] : allParts[0].slice(0, -1),
base: allParts[2],
ext: allParts[3],
name: allParts[2].slice(0, allParts[2].length - allParts[3].length)
ext: allParts[4],
name: allParts[3]
};
};



// Split a filename into [root, dir, basename, ext], unix version
// Split a filename into [dir, root, basename, name, ext], unix version
// 'root' is just a slash, or nothing.
var splitPathRe =
/^(\/?|)([\s\S]*?)((?:\.{1,2}|[^\/]+?|)(\.[^.\/]*|))(?:[\/]*)$/;
/^((\/?)(?:[^\/]*\/)*)((\.{1,2}|[^\/]+?|)(\.[^.\/]*|))[\/]*$/;
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These look like breaking changes to me, and I am not entirely sure if this fixes the DoS. I did a little work on this issue. It is tempting to fix the groups, the whitespace (\s\S), etc., but I found that the existing unit tests were incomplete (even if some are unrealistic).

I found that these tests needed to be added:

var regexDosFileNameLength = 50000;
var regexDosFileName = Buffer.alloc(regexDosFileNameLength, '/').toString() + 'file.txt';

[{ root: '/', dir: '/home/user/dir', base: 'file.txt', ext: '.txt', name: 'file' }, '/home/user/dir/file.txt/'],
[{ root: '/', dir: '/\n\thome/user/dir', base: 'file.txt', ext: '.txt', name: 'file' }, '/\n\thome/user/dir/file.txt/'],
[{ root: '/', dir: '/////////', base: 'file.txt', ext: '.txt', name: 'file' }, '//////////file.txt'],
[{ root: '/', dir: '/', base: '', ext: '', name: '' }, '//////////'],
[{ root: '/', dir: Buffer.alloc(regexDosFileNameLength - 1, '/').toString(), base: 'file.txt', ext: '.txt', name: 'file' }, regexDosFileName],
 ];

If you want these to be breaking changes, then fine. The regexDosFileNameLength is specifically to test the regex DoS.

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I can pass those tests with

var splitPathRe =
  /^((\/?)(?:[^\/]*\/)*)((\.{1,2}|[^\/]+?|)(\.[^.\/]*|))(?:(?<=^\/)|(?<!\/))[\/]*$/;`

return {
  // ...
  dir: allParts[0] === '/' ? allparts[0] : allParts[0].slice(0, -1),
  // ...
}

But as thrilling as it is to have a single regex handling the parsing, it'd be much wiser to clean up the parameter (e.g. by stripping trailing slashes, while retaining a leading slash) and keeping the regex simple.

And as for avoiding the ReDoS, my testing shows a significant improvement:

attack_str.length: 1970001: 332 ms
attack_str.length: 1980001: 359 ms
attack_str.length: 1990001: 385 ms
attack_str.length: 2000001: 295 ms

var posix = {};


Expand All @@ -67,19 +52,16 @@ posix.parse = function(pathString) {
);
}
var allParts = posixSplitPath(pathString);
if (!allParts || allParts.length !== 4) {
if (!allParts || allParts.length !== 5) {
throw new TypeError("Invalid path '" + pathString + "'");
}
allParts[1] = allParts[1] || '';
allParts[2] = allParts[2] || '';
allParts[3] = allParts[3] || '';


return {
root: allParts[0],
dir: allParts[0] + allParts[1].slice(0, -1),
root: allParts[1],
dir: allParts[0].slice(0, -1),
base: allParts[2],
ext: allParts[3],
name: allParts[2].slice(0, allParts[2].length - allParts[3].length)
ext: allParts[4],
name: allParts[3],
};
};

Expand Down
20 changes: 20 additions & 0 deletions redos.js
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@@ -0,0 +1,20 @@
var pathParse = require('.');

function build_attack(n) {
var ret = ""
for (var i = 0; i < n; i++) {
ret += "/"
}
return ret + "◎";
}

for(var i = 1; i <= 5000000; i++) {
if (i % 10000 == 0) {
var time = Date.now();
var attack_str = build_attack(i)
pathParse.posix(attack_str);
pathParse.win32(attack_str);
var time_cost = Date.now() - time;
console.log("attack_str.length: " + attack_str.length + ": " + time_cost+" ms")
}
}